Calculate the standard enthalpy change of formation, ∆fHө, of hydrogen sulfide using
the enthalpy change for Reaction 1, and the standard enthalpy changes of combustion
below.
Substance ∆cH ө / kJ mol−1
S(s) −296.8
H2(g) −285.8
2H2S(g) + 3O2(g) 2SO2(g) + 2H2O(l) ∆rH = –1125 kJ mol−1
I drew a hess cycle graph and i put my arrow inwards as I thought that even if we want to work out a value of formation our data is combustions so the arrows must point down \.
What i did was form a equation:
2x + (296x2) + (285.8x2) = -1125
2x = -2290.2
x = -1145.1 but this is wrong and the answer is -20.